Field of the Invention
The invention relates to a configuration for sealing a leadthrough gap between a wall and a shaft which is passed through the wall and can be set in rotation relative to the wall, including a sealing ring through which the shaft can be passed as well as a holder that can be firmly connected to the wall and has a cylindrical recess and a groove opening into the recess, the groove having a first groove surface and a second groove surface, between which the sealing ring is held, and a chamber that surrounds the sealing ring and can be filled with oil remaining in the groove.
Such a configuration is used, for example, on an electrical machine filled with hydrogen, in which the hydrogen is used in particular for cooling purposes. In that case, the configuration is used as part of a sealing system in order to seal a leadthrough of a rotatable shaft through a fixed casing of the machine and to prevent an escape of hydrogen into the surroundings of the machine. The use of the configuration on a large turbogenerator which is cooled solely with hydrogen or with hydrogen and water is of particular importance. Such a turbogenerator normally has a power output of 500 MVA and above and it has a sealed casing in which the hydrogen is under a pressure of 10.sup.5 Pa to 10.sup.6 Pa.
German Published, Non-Prosecuted Patent Application DE 37 23 729 A1 or UK Patent Application GB 0 760 781 A discloses a configuration of the type described at the outset above. Those documents also demonstrate possibilities for the further development of such a configuration. The first-mentioned document relates to the placemement of the sealing ring on a casing wall, in which case the sealing ring is not intended to be rotatable relative to the casing wall but to be easily displaceable for the purpose of centering. To that end, it is not disposed in a chamber but is held between the wall and a fastening plate by fastening bolts. Feed lines for oil are provided through the wall. In each case a line extension in the sealing ring is allocated to the feed lines. Each line extension leads into a corresponding annular groove in the sealing ring. The groove is to be allocated to the shaft to be sealed. Furthermore, an oil-leakage flow takes place at least to a limited extent between the sealing ring and the wall as well as between the sealing ring and the fastening plate. A sealing device, which is a lip seal, prevents larger quantities of oil from flowing off through a gap between the wall of the generator casing and the sealing ring. The pressure in the interior of the generator as well as the oil pressure load the sealing ring and press it against the fastening plate. In order to create a balance and to reduce the friction in gaps between the sealing ring and the fastening plate, annular relief oil grooves, to which oil can be fed, are provided in the fastening plate. The second-mentioned document in particular presents possibilities for feeding oil or another liquid for sealing and/or lubricating purposes to gaps between the sealing ring, the wall and the shaft.
A shaft seal for hydrogen-cooled turbogenerators is described in German Published, Non-Prosecuted Patent Application DE 37 12 943 A1, corresponding to U.S. Pat. No. 4,815,748. That shaft seal has a sealing configuration which is radially movable in a chamber and has two sealing rings enclosing the shaft, with at least one of the sealing rings being axially movable. Sealing oil is directed from the chamber to the shaft to be sealed through the use of a radial feed line which runs either through one sealing ring or between the two sealing rings. At least the second sealing ring has a radial line which is fluidically connected to a collecting space or a blind bore disposed in a surface of the chamber. In that way, some of the sealing-oil flow is diverted and fed back in the direction of the inner casing of the generator.
Swiss Patent 626 694, corresponding to U.S. Pat. No. 4,076,259, deals with a shaft seal, in particular for large compressor shafts. An annular gap remains between the shaft to be sealed and a sealing piston. The passing of the fluidic medium through that annular gap is to be restricted and throttled as far as possible by a helical groove cut in an inner wall of the sealing piston. The helical groove forms a labyrinth seal which, upon rotation of the shaft together with the labyrinth seal, produces a pumping action that prevents the sealing oil from penetrating into the interior of the compressor.
If a shaft having an increasing diameter is taken into account in the planning of a new turbogenerator, a problem arises from the fact that the dimensions of the gaps through which hydrogen could leak out of the casing of the turbogenerator along the shaft increase with the diameter of the shaft. As the demands on the sealing of the turbogenerator increase, that is reflected in the need to improve the sealing effect of a configuration of the type mentioned at the outset above. In many cases, an appropriate configuration is therefore often configured in such a way that it has two circuits for sealing oil which lie one behind the other along the shaft. In that case, a circuit facing the interior of the casing is intended to largely receive any leakages of hydrogen, and a circuit facing the exterior of the casing is intended to ensure that no air can penetrate into the casing. The outlay required to operate a configuration of such construction is very high, and accordingly the need has arisen to develop a configuration of the type mentioned at the outset above in such a way that it can be operated with a single circuit for sealing oil.
European Patent 0 542 751 B1, corresponding to U.S. Pat. No. 5,233,862, discloses a configuration for sealing a leadthrough gap between a casing wall and a shaft which is passed through the casing wall and can be set in rotation relative to the casing wall. In that configuration, the sealing ring, which slides on the rotating shaft without rotating with it, can be monitored in terms of its function. To that end, a torque which the rotating shaft exerts on the sealing ring is measured. If the torque exceeds a certain limit, it must be assumed that satisfactory lubrication of the sealing ring sliding on the shaft is no longer guaranteed and a problem is about to occur.
In the future it can be expected that an increasing pressure on the prices achievable on the market will require large dynamoelectrical machines to be simplified and reduced in price, in which case a leakage of hydrogen from a dynamoelectrical machine filled with hydrogen, which leakage can be tolerated operationally, will be increasingly less tolerable from the points of view of environmental protection and safety. Therefore, in a sealing system of the type described in the introduction, it is desirable to reduce the loading of the used oil with hydrogen to a minimum, which inevitably occurs when the oil comes in contact with the hydrogen. Hydrogen which has penetrated into oil cannot be recovered or can only be recovered at considerable cleaning cost and cannot be fed back to the electrical machine, and a loss of at least some of that hydrogen can scarcely be avoided somehow or other.
It may be stated in that connection that, in a sealing system which has two circuits in the manner described above for the oil used for sealing, a considerable input of hydrogen into at least one of the circuits is always to be expected. In view of the considerations referred to in the previous paragraph, it is therefore desirable to dispense with such sealing systems in the future and to manage with sealing systems having a single circuit for the oil in each case.